Showing papers on "Inertial wave published in 1981"

Observations and models of inertial waves in the deep ocean

Abstract: A study of the structure of the inertial peak in deep ocean kinetic energy is presented, based on records taken from Polymode arrays deployed in the western North Atlantic Ocean. Results are interpreted in terms of both local sources and turning point effects on internal waves generated at lower latitudes, and it is found that three classes of environment and their corresponding spectra emerge from peak height variations: (1) the 1500-m level near the Mid-Atlantic Ridge, with the greatest peak height of 18 dB; (2) the upper and deep ocean over rough topography and the deep ocean underneath the Gulf Stream, with the intermediate peak height of 11.5 dB; and (3) the deep ocean over smooth topography, with the lowest peak height of 7.5 dB. Using the globally valid wave functions obtained by Munk and Phillips (1968), frequency spectra near f are calculated numerically. The model is latitudinally dependent, with the frequency shift and bandwidth of the inertial peak decreasing with latitude.

Inertial Oscillations on the Continental Shelf of the Gulf of Lions—Observations and Theory

Abstract: Observations in the Gulf of Lions (northwestern Mediterranean Sea) in summer have shown that gusts of wind lasting a few days generate transient upwellings and inertial motions. Oscillations at the inertial frequency were observed in current meter data near the shore and at a frequency 10% greater in the temperature data. Vertical coherences in current meter data show a strong baroclinic mode at frequencies greater than inertial frequency. A simple one-dimensional two-layer transient model suggests that these motions are associated with two different physical processes. The first process describes the local response of the ocean to meteorological forcing, the second is associated with the propagation of long internal waves generated in the transient phase of the geostrophic adjustment process. As suggested by the model, the direction of propagation of the internal waves is computed from current and temperature data measured at one point and it is found that the shore is the source zone.

Solar cycle Lorentz force waves and the torsional oscillations of the sun

Abstract: A hypothesis is proposed and analyzed that the longitudinal component of the Lorentz force of the dynamo waves which well simulate the observed solar cycle can drive the recently observed torsional oscillations by Howard and LaBonte. The force component, which is reduced to a correlation between the toroidal and poloidal magnetic fields, consists of a nonwave part and a wave part. Only the nonwave part remains in the deep regions of the convection zone where the dynamo waves can propagate freely. The wave part, called here the Lorentz force waves, emerges only near the surface where the propagating dynamo waves are piled up and their wave profiles are deformed. Thus, the force waves are confined near the surface where the density is low and the moment of inertial is small. Hence, the oscillations are likely to be a phenomenon of rather shallow regions of the solar convection zone. Amplitude of force waves is estimated for typical values of the magnetic fields in the convection zone. It is concluded that driving the torsional oscillations by the force waves is possible in the solar convection zone. If this hypothesis is correct, the torsional oscillations can be the first concrete evidence that themore » magnetic force is indeed working on the global dynamics of the Sun.« less

The Propagation of Internal Waves in a Geostrophic Current

Abstract: The paper presents the WKB theory of internal wave propagation in a large-scale geostrophic mean flow with vertical as well as horizontal shear. As an application a mean flow with isopycnals having constant slope but arbitrary spacing is considered and the behavior of waves at turning points and critical layers is discussed. In particular, it is shown that horizontal variations of the mean flow shift the critical layer to the interior of the wave guide, i.e., away from ω02 = f2, where ω0 is the intrinsic frequency, and produces a valve effect at the critical layer which can be penetrated by a wave incident from one side while incidence from the other side results in absorption.

The Erosion of a Thermocline

Abstract: Measurements of winds, currents and temperature are used to describe the response of the Baltic Sea to the passage of a sequence of severe storms during the BOSEX-Experiment in September 1977. Before the onset of the storms the thermocline was at a depth of ∼25 m. The storms deepened the mixed surface layer and redistributed the heat content. The storms generated strong inertial waves and vertical current shears, which reduced the Richardson number within the thermocline to values of ∼0.25. The non-linearity of the inertial waves in this area of variable depth is demonstrated. The response of the Baltic Sea to the meteorological conditions has been modeled numerically by means of a semispectral model. The theoretical results are compared to the observations and lead to the same conclusion, that the erosion of the thermocline is due to the strong shears of the inertial waves.

Structure of the Flow within the Coastal Boundary Layer of the Great Lakes

Abstract: Properties of the nearshore flow have been observed in some detail in Douglas Point, Lake Huron. Time series flow data obtained from a network of current meters deployed in a coastal chain perpendicular to the local shoreline have been analyzed to resolve the mean flow properties, horizontal turbulence characteristics and the kinetic energy (in the mean flow and fluctuations) within the coastal boundary layer. The variability of these parameters as a function of the distance from shore for an episode during which persistent short-parallel currents prevailed for several days has revealed two distinct boundary layers, an inner boundary layer dominated by bottom and shore friction (FBL—frictional boundary layer) and an outer boundary layer as a consequence of the adjustments of inertial oscillations to the lateral boundary (IBL—inertial boundary layer). If one takes the width of the frictional boundary layer as the distance to the point where the kinetic energy of currents peak, it is ∼2 km at Dougl...

Wind‐driven inertial oscillations of large spatial coherence

Abstract: Inertial oscillations in current records collected from May to September, 1977, at ten mooring sites 20–300 km apart in the semi‐enclosed sea off northwest British Columbia are analysed. Near‐surface oscillations were wind‐driven, clockwise rotary and circularly polarized; near‐bottom oscillations at depths of 155–330 m were clockwise rotary, less than 10% of near‐surface amplitudes, highly elliptical and poorly correlated with surface winds. In the open southwest sector of the region, near‐surface spectra possessed well‐defined peaks centred roughly 3.5% above the local inertial frequency (f), whereas spectra for the semi‐enclosed northern sector had broad peaks centred at f. The peak spectral frequency at the southeast corner of the mooring array was 6.5% below f and is linked to a Doppler shift by mean flow advection of comparatively high wavenumber inertial oscillations. A particularly vigorous wind‐generated surface “event” in mid‐June was coherent to 99% confidence over a distance of 300 km...

A simple physical model for the terrestrial dynamo

Abstract: The strength of the earth's magnetic field results from an equilibration between rates of buoyant energy production and Ohmic dissipation. Changes in magnetic field, in particular the long term changes in dipole moment, provide an indication of changes in core energy sources, and so become critical data for understanding the evolution of both the core and deep mantle. A simple physical model is proposed to establish a connection between dipole moment behavior and production of buoyancy within the core. The model rests on two hypotheses: (1) magnetism is generated by small scale, rotation dominated turbulence consisting of a field of propagating inertial waves, and (2) the turbulence is supported by a flux of buoyancy, thermal or compositional, originating either at the core-mantle or inner core boundary. The efficiency with which wave kinetic energy is converted to magnetic energy is determined by the wave helicity—the correlation between velocity and vorticity. The wave helicity is non-zero if there exists a preferred propagation direction. Negative buoyancy generated at the mantle-core boundary leads to propagation radially inward; positive buoyancy generated at the inner core boundary leads to radially outward propagation. Using parameters appropriate for the earth's core, we find that the inertial wave dynamo dissipates 8 × 1011 W in generating a magnetic field equal to the present terrestrial field. Four energy sources are considered: decay of potassium 40, secular cooling, inner core growth, and differentiation of the core from the mantle. Any of these sources can reasonably support the turbulent dynamo for much of the earth's history.

Design Curves for Hinged Wavemakers: Theory

Abstract: Dimensionless theoretical design curves for hinged wavemakers of variable draft are extended, within the limits of linearized potential wave theory, to wave flume geometries consisting of two constant depth domains separated by a gradually sloping transition region. These design curves are examined for the following: hydrodynamic pressure moment, moment arm, relative moment phase angle, and the ratio of the wavemaker stroke to the propagating wave height. The dimensionless design curves are shown to demonstrate the effects of wave flume and wavemaker geometry on the minimum inertial wave pressure moment on the wavemaker flap better than tabular lookup methods. The effects of nondimensional wavemaker parameters on the dimensionless wavemaker power curves are explored, and they are compared to the energy flux in a propagating periodic wave. Convergence of the eigenfunction expansion for the wavemaker velocity for hinged wavemakers of variable depth is examined numerically.

Note on the analogy between inertial and electromagnetic forces

Abstract: The authors point out that the inertial force F3 = −mω×r is completely analogous to the force associated with an induced emf. (AIP)

An Experimental Study of Gravity-Inertial Waves and Wind-Induced Kelvin-Type Upwellings in a Rotating System

Abstract: Large-amplitude gravity-inertial waves have been observed in stratified seas. These waves, of a shorter period than the Coriolis period, are linked to a gust of wind. Numerous theories have been proposed to explain these waves but, up to now, they have not been verified experimentally in a rotating system. On the large rotating platform in Grenoble, the author has built a large tank (8 m × 2 m × 0.6 m) equipped with a wind tunnel. By strictly controlling the main parameters (speed of rotation of the platform, and thus Coriolis period, intensity and duration of the impulsional wind, height and density of the two fluid layers) he has studied and analyzed the variations in height of the interface between the two fluids. Here, the author's work is placed in the general context of various studies of this phenomenon, and some analytical developments are presented within the general hypothesis first used by Crepon (1969a,b). The experimental facilities are described briefly and a preliminary explanation...

Waves at 200 mb during GATE

Abstract: A 200 mb data set obtained during the GATE experiment of the 1974 summer for the period 15 June-23 September and covering the global tropics 25°S to 45°N has been analyzed to determine the presence of certain wave modes in the tropical troposphere. The wavenumber-frequency method of analysis was used and the flow separated into eastward and westward moving waves. Results show what could be identified as Kelvin, Rossby and mixed Rossby- gravity waves. The period of the Kelvin wave was longer than that normally reported for similar waves in the stratosphere.

Lagrangian Partial-Inertial Oscillations, and Subtropical and Low-Level Monsoon Jet Streaks

Abstract: Jet streaks (local wind maxima) are prominent features of current systems both in the high and lowtroposphere. As particles in the core of the current flow through them, they experience cyclical velocityoscillations whose characteristics (period, dimensions and form of the wave described by a trajectory) arerelated to the way in which the geostrophic wind varies along the current. Although there is considerablevariation, the modal period is nearly semi-inertial (twice the inertial period). Two special cases are examined. First, jet streaks in the mean winter subtropical jet stream (STJ) aredemonstrated to be approximate semi-inertial oscillations and also planetary waves, a coincidence shownto be unique to the subtropical latitude. STJ waves are distinctive from middle-latitude Rossby waves inthe respects that they are dominated by departures from gradient-wind motion and also have dissimilardivergence distributions. Second, the mean July low-level monsoon jet over the Arabian Sea, with anoscilla...

Envelope soliton solution for finite amplitude equatorial waves

Abstract: Using shallow water equations on an equatorial beta plane, the nonlinear dynamics of the equatorial waves is investigated. A general mathematical procedure to study the nonlinear dynamics of these waves is developed using the asymptotic method of multiple scales. On faster temporal and spatial scales the equations describe the equatorial wavesviz, the Rossby waves, Rossby gravity waves, the inertia gravity waves and the Kelvin waves. Assuming that the amplitude of these waves are functions of slower time and space scales, it is shown that the evolution of the amplitude of these waves is governed by the nonlinear Schrodinger equation. It is then shown that for the dispersive waves like Rossby waves and Rossby-gravity waves, the envelope of the amplitude of the waves has a ‘soliton’ structure.

Vortex Breakdown Phenomena in a Circular Pipe : 1st Report, Modes of Stationary Breakdown

Abstract: The purpose of this investigation is to give a theoretical explanation for the vortex breakdown phenomena of a swirling flow in a pipe. In the proposed mathematical model, the mean flow is assumed to be a rigidly rotating one (constant angular velocity) with uniform axial velocity. It is found that the internal wave (inertial wave), which may occur in the swirling flow, plays a significalt role in the breakdown phenomena. An integer parameter in the formula describing the internal wave, has a close relation with the structural mode of breakdown. Thus, the first three values of the parameter, 0, 1, 2, correspond to the typical three observed types of breakdown, axisymmetric, spiral, and double helix, respectively. The present study concerns only time-independent types of these phenomena. The time-dependent ones will be discussed in another paper.

An Experimental Study of Inertial Waves in a Rotating Fluid Cylinder During Spin-Up of the Fluid from Rest.

Abstract: : This research has been primarily concerned with the excitation and detection of inertial waves in a fluid contained in a rotating cylindrical cavity during spin-up of the fluid from rest Application of this work is to the study of fluid filled projectiles and their stability in free flight It is well known that a projectile containing fluid will be subject to instability if its nutational frequency is near one of the eigenfrequencies of the contained fluid Our work has centered on finding these time dependent eigenfrequencies for a fluid which completely fills a cylindrical cavity Also of interest in the application of our work is the rate at which these waves decay once they are excited during the spin-up period Included in our experimental work was a study of decay rates for several inertial waves during spin-up from rest (Author)